High-Yield Synthesis Single-Walled Carbon Nanotubes By Chemical Vapor Decomposition

High yield growth of high purity SWNTs is the critical step towards their unique properties and functional applications, which has been attached great attention in the past decades in the field of new material synthesis. By the catalytic chemical vapor decomposition method, in use of ethylene as the carbon source and magnesia-supported metal (Fe, Co, Ni) and bimetallic (Fe-Mo, Fe-Co) catalysts that were prepared by impregnation and co-precipitation of their precursors, we successfully synthesized well crystallized SWNTs in a high yield and high purity. The syntheses were conducted in a horizontal furnace with a quartz tube reactor between 750~950°C using argon as the carrying gas, with the reaction typically lasted for 5~30min. The products were systematically analyzed by Scanning Electronic Microscope (SEM), High Resolution Transmission Electronic Microscopy (HRTEM), Raman spectroscopy and Thermal Gravity Analysis (TGA). Results showed that the concentration of SWNTs in the products increased with the synthesis temperatures from 750°C to 950°C. The co-precipitated Fe/MgO catalysts provided smaller and homogeneous phase of the catalysts, which therefore, enhanced the growth of SWNTs compared to the impregnation route prepared catalysts. By optimizing the reaction temperature to 850°C, reaction time for 10 min and the ethylene flow rate to 75 ml/min, we achieved a carbon yield as high as 4129 wt % (the weight ratio of the carbon yield and the metal catalyst) which is 7.5 times that yield reported earlier by the similar synthesis system. TEM observation indicated that the SWNTs content in the product was 69 wt %, while Raman analysis showed a high degree of crystallinity of the SWNTs, with the ratio of the'G'band and'D'band in intensity of IG/ID=10. Furthermore, introducing Co into the catalysts via co-precipitation at the mole ratio of Fe:Co:MgO=1:0.5:100 improved the purity of the SWNT products while a higher Co input reduced the carbon yield. Finally, the growth mechanism of SWNTs in the above synthesis processes was discussed based on the experimental results.